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Chapter 10 Respiration During Exercise

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1 Chapter 10 Respiration During Exercise
EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 5th edition Scott K. Powers & Edward T. Howley

2 Introduction The Respiratory System
Provides a means of gas exchange between the environment and the body Plays a role in the regulation of acid-base balance during exercise

3 Objectives Explain the principle physiological function of the pulmonary system Outline the major anatomical components of the respiratory system List major muscles involved in inspiration and expiration, at rest and during exercise Discuss the importance of matching blood flow to alveolar ventilation in the lung Explain how gases are transported across the blood-gas interface in the lung

4 Objectives Discuss the major transportation modes of O2 and CO2 in the blood Discuss the effects of  temp,  pH, and  levels of 2-3 DPG on the oxygen-hemoglobin dissociation curve Describe the ventilatory response to constant load, steady-state exercise

5 Objectives Describe the ventilatory response to incremental exercise
Identify the location and function of chemoreceptors and mechanoreceptors that are thought to play a role in the regulation of breathing Discuss the neural-humoral theory of respiratory control during exercise

6 Respiration Pulmonary respiration
Ventilation (breathing) and the exchange of gases (O2 and CO2) in the lungs Cellular respiration Relates to O2 utilization and CO2 production by the tissues This chapter is concerned with pulmonary respiration, and “respiration” will be used to mean such

7 Function of the Lungs Primary purpose is to provide a means of gas exchange between the external environment and the body Ventilation refers to the mechanical process of moving air into and out of lungs Diffusion is the random movement of molecules from an area of high concentration to an area of lower concentration

8 Major Organs of the Respiratory System
Fig 10.1

9 Position of the Lungs, Diaphragm, and Pleura
Fig 10.2

10 Conducting and Respiratory Zones
Conducting zone Conducts air to respiratory zone Humidifies, warms, and filters air Components: Trachea Bronchial tree Bronchioles Respiratory zone Exchange of gases between air and blood Components: Respiratory bronchioles Alveolar sacs

11 Conducting & Respiratory Zones
Fig 10.2

12 Pathway of Air to Alveoli
Fig 10.4

13 Mechanics of Breathing
Inspiration Diaphragm pushes downward, lowering intrapulmonary pressure Expiration Diaphragm relaxes, raising intrapulmonary pressure Resistance to airflow Largely determined by airway diameter

14 The Mechanics of Inspiration and Expiration
Fig 10.6

15 Muscles of Respiration
Fig 10.7

16 Pulmonary Ventilation (V)
The amount of air moved in or out of the lungs per minute Product of tidal volume (VT) and breathing frequency (f) V = VT x f

17 Pulmonary Ventilation (V)
Dead-space ventilation (VD) “Unused” ventilation Does not participate in gas exchange Anatomical dead space: conducting zone Physiological dead space: disease Alveolar ventilation (VA) Volume of inspired gas that reaches the respiratory zone V = VA + VD

18 Pulmonary Volumes and Capacities
Measured by spirometry Vital capacity (VC) Maximum amount of air that can be expired following a maximum inspiration Residual volume (RV) Air remaining in the lungs after a maximum expiration Total lung capacity (TLC) Sum of VC and RV

19 Pulmonary Volumes and Capacities
Fig 10.9

20 Partial Pressure of Gases Dalton’s Law
The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently The partial pressure of oxygen (PO2) Air is 20.93% oxygen Expressed as a fraction: Total pressure of air = 760 mmHg PO2 = x 760 = 159 mmHg

21 Diffusion of Gases Fick’s law of diffusion
The rate of gas transfer (V gas) is proportional to the tissue area, the diffusion coefficient of the gas, and the difference in the partial pressure of the gas on the two sides of the tissue, and inversely proportional to the thickness. V gas = A T x D x (P1-P2) V gas = rate of diffusion D = diffusion coefficient of gas A = tissue area P1-P2 = difference in partial pressure T = tissue thickness

22 Partial Pressure and Gas Exchange
Fig 10.10

23 Blood Flow to the Lung Pulmonary circuit
Same rate of flow as systemic circuit Lower pressure Fig 10.11

24 Blood Flow to the Lung When standing, most of the blood flow is to the base of the lung Due to gravitational force Fig 10.12

25 Ventilation-Perfusion Relationships
Ventilation/perfusion ratio Indicates matching of blood flow to ventilation Ideal: ~1.0 Base Overperfused (ratio <1.0) Apex Underperfused (ratio >1.0)

26 Ventilation/Perfusion Ratios
Fig 10.13

27 O2 Transport in the Blood
Approximately 99% of O2 is transported in the blood bound to hemoglobin (Hb) Oxyhemoglobin: O2 bound to Hb Deoxyhemoglobin: O2 not bound to Hb Amount of O2 that can be transported per unit volume of blood in dependent on the concentration of hemoglobin

28 Oxyhemoglobin Dissociation Curve
Fig 10.14

29 O2-Hb Dissociation Curve: Effect of pH
Blood pH declines during heavy exercise Results in a “rightward” shift of the curve Bohr effect Favors “offloading” of O2 to the tissues Fig 10.15

30 O2-Hb Dissociation Curve: Effect of Temperature
Increased blood temperature results in a weaker Hb-O2 bond Rightward shift of curve Easier “offloading” of O2 at tissues Fig 10.16

31 O2-Hb Dissociation Curve: 2-3 DPG
RBC must rely on anaerobic glycolysis to meet the cell’s energy demands A by-product is 2-3 DPG, which can combine with hemoglobin and reduce hemoglobin’s affinity of O2 2-3 DPG increase during exposure to altitude At sea level, right shift of curve not to changes in 2-3 DPG, but to degree of acidosis and blood temperature

32 O2 Transport in Muscle Myoglobin (Mb) shuttles O2 from the cell membrane to the mitochondria Higher affinity for O2 than hemoglobin Even at low PO2 Allows Mb to store O2

33 Dissociation Curves for Myoglobin and Hemoglobin
Fig 10.17

34 CO2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%)
Bicarbonate (70%) CO2 + H2O  H2CO3  H+ + HCO3- Also important for buffering H+

35 CO2 Transport in Blood Fig 10.18

36 Release of CO2 From Blood
Fig 10.19

37 Rest-to-Work Transitions
Initially, ventilation increases rapidly Then, a slower rise toward steady-state PO2 and PCO2 are maintained Fig 10.20

38 Exercise in a Hot Environment
During prolonged submaximal exercise: Ventilation tends to drift upward Little change in PCO2 Higher ventilation not due to increased PCO2 Fig 10.21

39 Incremental Exercise Linear increase in ventilation
Up to ~50-75% VO2max Exponential increase beyond this point Ventilatory threshold (Tvent) Inflection point where VE increases exponentially

40 Ventilatory Response to Exercise: Trained vs. Untrained
In the trained runner, decrease in arterial PO2 near exhaustion pH maintained at a higher work rate Tvent occurs at a higher work rate Fig 10.22

41 Ventilatory Response to Exercise: Trained vs. Untrained
Fig 10.22

42 Exercise-Induced Hypoxemia
1980s: 40-50% of elite male endurance athletes were capable of developing 1990s: 25-51% of elite female endurance athletes were also capable of developing Causes: Ventilation-perfusion mismatch Diffusion limitations due to reduce time of RBC in pulmonary capillaries due to high cardiac outputs

43 Control of Ventilation
Respiratory control center Receives neural and humoral input Feedback from muscles CO2 level in the blood Regulates respiratory rate Fig 10.23

44 Input to the Respiratory Control Centers
Humoral chemoreceptors Central chemoreceptors Located in the medulla PCO2 and H+ concentration in cerebrospinal fluid Peripheral chemoreceptors Aortic and carotid bodies PO2, PCO2, H+, and K+ in blood Neural input From motor cortex or skeletal muscle

45 Effect of Arterial PCO2 on Ventilation
Fig 10.24

46 Effect of Arterial PO2 on Ventilation
Fig 10.25

47 Ventilatory Control During Exercise
Submaximal exercise Linear increase due to: Central command Humoral chemoreceptors Neural feedback Heavy exercise Exponential rise above Tvent Increasing blood H+

48 Ventilatory Control During Submaximal Exercise
Fig 10.26

49 Effect of Training on Ventilation
Ventilation is lower at same work rate following training May be due to lower blood lactic acid levels Results in less feedback to stimulate breathing

50 Effects of Endurance Training on Ventilation During Exercise
Fig 10.27

51 Do the Lungs Limit Exercise Performance?
Low-to-moderate intensity exercise Pulmonary system not seen as a limitation Maximal exercise Not thought to be a limitation in healthy individuals at sea level May be limiting in elite endurance athletes New evidence that respiratory muscle fatigue does occur during high intensity exercise

52 Chapter 10 Respiration During Exercise

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